Renormalize rotation in 2D integration and clean up renormalize

[Jondolf]

Objective

Currently, only 3D rotation is renormalized after position integration. However, 2D rotation can also become denormalized over time, sometimes causing crashes with debug_assertions.

Solution

Add fast_renormalize for 2D Rotation and renormalize 2D rotations after position integration.

I also renamed the 3D Rotation::renormalize method to fast_renormalize, and made it return the value instead of mutating self, to match Bevy 0.15.

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Migration Guide

The 3D Rotation::renormalize method has been renamed to fast_renormalize, and it returns the value instead of mutating self. This was changed to match Bevy 0.15.